Low-voltage, medium-voltage and high-voltage switchgear assemblies have the task of distributing the energy flow and of ensuring safe operation. In the improbable case of an internal fault (fault arc), installation safety and personal safety must also be ensured. A fault arc which occurs within a switchgear assembly would produce a sharp pressure rise of the gas, due to the temperature of the gas, within a time period of a few milliseconds, which can lead to the switchgear assembly being destroyed by explosion. Measures are therefore adopted in order to dissipate the pressure as quickly as possible. Furthermore, an arcing fault is intended to be restricted to the relevant area, and must not endanger the operator.
The creation of fault arcs can be restricted by suitable design, such as by internal subdivision of the switch panel (compartmentalization), for example. For this purpose, the individual switch panels of a switchgear assembly can have pressure-relief openings or pressure-relief channels, via which the gas can flow out into the surrounding area. The effects of a fault arc can therefore be limited by reducing the arc duration.
This effect can be achieved with the aid of suitable sensors which react to light, temperature or pressure and which release the upstream circuit breaker, such as the feed switch. This arrangement results in arcing times of 40 ms to 80 ms (a fault arc which burns in a gas atmosphere air or in some other insulating gas within a subdivision, that is to say a compartment (encapsulation) or in a solid (boundary layer)). However, this arrangement has the disadvantage that the greatest mechanical load occurs just after approximately 10 ms, and only the thermal load is reduced. This arrangement involves a generally robust and costly configuration of the design of a switchgear assembly, of encapsulation or of a solid-insulated system.
In order to overcome an internal fault (fault arc) even while the pressure is rising, a switching device is a switching device is provided to switch within a few milliseconds. The inclusion of such a switching device is known as a so-called short-circuiting system. Exclusively three-phase short-circuiting devices such as these are known to switch in air or SF6. In any case, the switching rating and isolation capability are reduced because of the high inrush current on repeated switching. In contrast, when using a vacuum interrupter chamber, these electrical characteristics remain virtually unchanged as the number of switching operations increases.
A range of solutions relating to this issue have been proposed in the prior art.
DE 199 21 173 A1 discloses a short-circuiting system which contains a vacuum interrupter chamber in each individual phase or between the phases, based on the principle of a “switched vacuum interrupter chamber” and “triggered vacuum gap”.
DE 199 16 329 A1 discloses a short-circuiting device for a fault arc protection apparatus, for use in installations for distribution of electrical power with a gas generator and a short-circuiting piston, which is driven directly by the gas generator, for electrical connection of connecting rails to a connection rail which is intended to be compact, to have good piston guidance and to be suitable for use with gas generators. The piston guidance is achieved by the short-circuiting piston being guided and held in a connection rail. In addition, the gas generator is embedded in a holding part which has an initial volume, is composed of insulating material, and is directly attached to the connection rail.
DE 197 468 15 A1 discloses a similar fault-arc protection apparatus for use in installations for distribution of electrical power with a gas generator, in which the short-circuiting piston, which is driven by the gas generator, carries out an optimum sudden movement, and is at the same time secured for transportation, independently of manufacturing tolerances, with a further objective of the gas generator being securely mounted. This objective is achieved by the short-circuiting piston being provided with at least one O-ring as a seal. In addition, the upper face of the short-circuiting piston rests flush on a pressure membrane in the unreleased state, such that a vacuum would be created in the event of a piston movement in the unreleased state, and would move the short-circuiting piston back to its rest position.
However, there are drawbacks associated with the second and third cited prior art references for switchgear assemblies, including medium-voltage switchgear assemblies, for example. In conjunction with the upstream circuit breaker, known short-circuiting devices switch too slowly. Because of their three-phase design, they are generally also technically too complicated and costly. During a switching process, these short-circuiting devices connect the previously live current path in all three phases to ground, or else between the individual phases. This in turn involves a compact, complex ground current path for carrying the generally high fault current for a short time. Furthermore, the current results in a decrease in the switching rating and the isolation capability over the lifespan of the short-circuit devices.